Shedding is the well known operation during weaving when the warp yarn harnesses are raised and lowered to create an opening in the shape of a "V", called the shed, between layers of warp yarn. This occurs as some harnesses are raised while alternate harnesses are lowered. The shuttle passes through the "V"-shaped opening and inserts a pick of filling. The harnesses then reverse, capturing the previous pick and forming a new opening for a subsequent pick.
While shedding motions may vary widely from one type of loom to another, they generally fall into one of two categories. Either the harnesses are biased upwardly by a spring and pulled downwardly by some type of lever mechanism, or else the harnesses are biased downwardly and pulled upwardly by a dobby mechanism. Therefore, most of the shedding mechanisms in the prior art rely on springs or a combination of springs and gravity to urge the harnesses in one direction. Such devices may be satisfactory when used in connection with fly shuttle or rapier (shuttleless) looms which operate at speeds up to 300-400 picks per minute. However, with the advent of air jet looms and speeds in the range of 600 picks per minute, problems are envisioned by the previous known shedding mechanisms which rely heavily on springs.
It should be pointed out here that there are some examples in the prior art of shedding mechanisms which do not rely on springs and/or gravity to drive the harnesses, but are to the contrary positively driven in both stroke directions. These examples include the drive mechanisms disclosed in U.S. Pat. Nos. 4,337,801 issued July 6, 1982; 2,408,645 issued Oct. 1, 1946; and 3,168,116 issued Feb. 2, 1965. In each of the aforementioned approaches, the shedding mechanism positively drives the harnesses during the upward stroke as well as during the downward stroke. However, each of them involve a rather complicated system of linkages which would make a smooth stroke at high speeds very difficult, if not impossible. In addition, each approach set forth in the above-identified patents utilizes a crank mounted at the stub end of some auxiliary shaft as the operative member which synchronously connects the movement of the loom mechanism to the the harnesses. In many types of looms, e.g. Draper looms, there is an existing cam shaft and the attachment is made beneath the central portion of the loom. In such situations it is not possible to connect a crank to the cam shaft, because the cam shaft continues across the entirety of the width of the loom. Therefore a cam of the type where followers engage one or more peripheral drive surfaces must be used. "Positive drive," which occurs where the drive surface always engages one or more followers, in such devices is not known to applicant. In a further U.S. patent, U.S. Pat. No. 3,108,617 to Nichols, there is shown a selvage harness control which is operated by a facing cam, which in turn is operated from a pinion on the main cam shaft; however, this is a totally different environment.
In the present invention, on the other hand, the ultimate object is to provide a shedding mechanism that will effect a smooth, consistant, positive harness motion even at speeds in the range of 600 picks per minute. Toward this end, there are several criteria which must be addressed in order to achieve the overall goal of smooth continuous harness motion. These criteria include a positive drive motion, simplicity, and assurance of synchronization of harness motion. In an effort to make the operation of the harnesses as smooth as possible, it was decided that the mechanism should be as simple as possible and the number of operative links in the mechanism kept to a minimum. Thus, the shedding mechanism of the present invention is operated directly from a control cam on the main cam shaft or an auxiliary cam shaft. This control cam is double-landed (two drive surfaces) so that the synchronization of the upper harness and lower harness strokes may be facilitated. A pair of yokes or actuator means connect the double-landed cam to a pair of L-shaped treadles, one of which operates one set of harnesses and the other of which operates the other set of harnesses. Each yoke includes a bifurcated portion at one end which substantially surrounds the eccentric drive surface of the cam and includes followers attached thereto. Such a construction is critical to the smooth operation of the shedding mechanism so that no matter whether the harnesses are undergoing an upward stroke or a downward stroke, the drive surface of the cam is always engaged positively with one or more of the followers in the yoke. Thus there is no possibility that the followers will leave the surface of the cam, and a much smoother, reliable stroke is obtained.
The opposite end of each yoke is attached to one leg of one of the L-shaped treadles. The other leg of the treadle is connected to one of the harnesses by means of a connecting rod. Thus, as the cam rotates, it causes the opposite end of the yoke to reciprocate, which in turn, causes the treadles to pivot about the axis of a rocker shaft. In a preferred embodiment the set of treadles connected to the yokes are, in turn, connected to another set of treadles, horizontally spaced from the first set. Each set of treadles is connected to one end of a set of harnesses. The resulting motion of the two sets of treadles raises and lowers the harnesses synchronously in a very regular, smooth, continuous motion. A slot is provided in the leg of the treadle to which the yoke is attached, so that the opening between the upper and lower warp yarns of the shed may be varied. The double-landed cam is fabricated in two halves, each half being assembled on opposite sides of the cam shaft, and the halves bolted together. A pair of tightening collars then are applied to the cams to tighten them securely to the cam shaft without the use of set screws thereby facilitating axial and rotational positioning of the cam on the shaft relative to other loom system functions.
It is therefore a principal object of the present invention to provide a shedding mechanism for weaving looms, which shedding mechanism provides a smooth, regular harness stroke even at high speeds.
Another object of the present invention is to obtain the smooth, regular harness stroke as described hereinabove with a very simple mechanism which is driven from the cam shaft or an auxiliary cam shaft of the loom.
Yet another object of the present invention is to provide a shedding mechanism of the type described in which each actuator contains a plurality of followers, one or more of which are in continuous engagement with the drive surface of the drive cam as it rotates.
Still another object of the present invention is to provide a shedding mechanism of the type described in which the harnesses are positively driven both in their upward stroke and in their downward stroke.